Hi All, One problem here is WHAT shielding effectiveness is being measured. Often a thin material that has an advertised shielding effectiveness if 80 dB turns out to be much less in a real application. The issue here is that the advertised spec is likely to be a far field plane wave spec whereas in real equipment the shield may not be illuminated by a plane wave. Often the illumination is from a local magnetic field. I have seen lots of 90+dB plane wave material measure out at ~10 dB to a magnetic field. One way to measure shielding effectiveness this way is described in one of my monthly Technical Tidbits. The article is:
http://www.dsmith.org/tt080100.htm An application of this method to cellphone gaskets is: http://www.dsmith.org/pdf/emc96.pdf Doug Jacob Schanker wrote: > > Chris: > > Your comment about metallic coatings on display windows not being useful for > RF shielding made me sit straight up (from my usual scrolling the email > slouch). > > You probably know that there are several vendors who market metallic coated > plastics for display windows and certainly imply, if not downright claim, > EMC shielding properties. I recall seeing dB shielding figures at RF given > in the data sheets. I recommended them for use in my previous position (yes, > me too) but did not get to see the results of the implementation. > > I'd like to hear from the others on the list what experiences they may have > had with using the plastic shielding windows compared to the embedded > metallic mesh variety. > > Regards, > > Jack > > Jacob Z. Schanker, P.E. > 65 Crandon Way > Rochester, NY 14618 > Phone: 716 442 3909 > Fax: 716 442 2182 > [email protected] > > ----- Original Message ----- > From: Chris Maxwell <[email protected]> > To: <[email protected]>; <[email protected]>; > <[email protected]> > Sent: Friday, June 29, 2001 10:01 AM > Subject: RE: LCD Monitors etc. > > > > > I have had similar experience. Not experimenting with LCD's themselves, > but > > testing products with LCD's. Most of the ones that I have experience > with > > have a metal back plate. It seems that it's important to bond this plate > > peripherally to your casework shielding. That keeps the circuits behind > the > > display from radiating around it. It doesn't seem as though the displays > > themselves (in my limited experience) cause much trouble at all, even with > > Class B stuff. > > > > We once experimented with ITO (Indium Tin Oxide) coatings on the display > > window to see if it would lower emissions. It didn't, but it did > increase > > cost. We bagged it. As a side comment, it seems like ITO is conductive > > enough for static dissipation, but not for shielding. So, if you ever did > > need to shield an LCD, you would probably be limited to windows that use > > metallic mesh sandwiches. > > > > Chris Maxwell > > Design Engineer - > > NetTest Optical Division > > email [email protected] > > phone +1 315 266 5128 > > fax +1 315 797 8024 > > NetTest > > 6 Rhoads Drive, > > Utica, NY 13502 USA > > web www.nettest.com > > > > > > > -----Original Message----- > > > From: [email protected] [SMTP:[email protected]] > > > Sent: Friday, June 29, 2001 7:02 AM > > > To: [email protected]; [email protected] > > > Subject: Re: LCD Monitors etc. > > > > > > > > > George, > > > > > > I did a number of experiments on 15" monitors for a machine HMI. They > are > > > indeed quiet, but there is quite a difference between manufacturers..... > > > > > > Most of the problems I had to fix were related to leakage through the > > > display > > > from circuitry behind it. > > > > > > Derek. > > > > > > ------------------------------------------- > > > This message is from the IEEE EMC Society Product Safety > > > Technical Committee emc-pstc discussion list. > > > > > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > > > > > To cancel your subscription, send mail to: > > > [email protected] > > > with the single line: > > > unsubscribe emc-pstc > > > > > > For help, send mail to the list administrators: > > > Michael Garretson: [email protected] > > > Dave Heald [email protected] > > > > > > For policy questions, send mail to: > > > Richard Nute: [email protected] > > > Jim Bacher: [email protected] > > > > > > All emc-pstc postings are archived and searchable on the web at: > > > http://www.rcic.com/ click on "Virtual Conference Hall," > > > > ------------------------------------------- > > This message is from the IEEE EMC Society Product Safety > > Technical Committee emc-pstc discussion list. > > > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > > > To cancel your subscription, send mail to: > > [email protected] > > with the single line: > > unsubscribe emc-pstc > > > > For help, send mail to the list administrators: > > Michael Garretson: [email protected] > > Dave Heald [email protected] > > > > For policy questions, send mail to: > > Richard Nute: [email protected] > > Jim Bacher: [email protected] > > > > All emc-pstc postings are archived and searchable on the web at: > > http://www.rcic.com/ click on "Virtual Conference Hall," > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > http://www.rcic.com/ click on "Virtual Conference Hall," -- ------------------------------------------------------- ___ _ Doug Smith \ / ) P.O. Box 1457 ========= Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-----( ) | o | Email: [email protected] \ _ / ] \ _ / Website: http://www.dsmith.org ------------------------------------------------------- ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
